Means and method for signaling by electric waves



March 1, 1932. 1.. J. SIVIAN 1,847,142

MEANS AND METHOD FOR SIGNALING BY ELECTRIC WAVES Original Filed Dec. 5, 1923 fiver/(01 L eon JJ/ wan hy KM/$1M A773 plify the received ener plifier and to prevent slnging in the amplifier.

Patented Mar. 1, 1932 cm STATES PATENT OFFICE LEON 3. SIVIAN, OF EAST ORANGE, NEW JERSEY, ASSIGNOR T0 WESTERN ELEUIBIO V COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK MEANS AND METHOD FOR SIGNALING BY ELECTRIC WAVE Application filed December 5, 1928, Serial No. 678,650. Renewed February 11, 1930.-

This invention relates to means and methods for signaling byelectric waves.

Hitherto, in electric wave signaling as, for example, in telegraphy and telephony, sys- 5 tems have been devised wherein a constant frequency wave or carrier is generated and varied in amplitude in accordance with signal variations to be transmitted. This method of modulation as is now well known, produces side bands having frequencies which are represented by the sum and difference of the carrier and modulatin frequencies. Al-

though the frequencies 0 these side bands differ from the carrier they remain constant in value as long as the carrier and modulating frequencies are constant. The present invention comprlses an 1mproved modulating method and means for its accomplishment, wherein a substantially constant amplitude wave is modulated as a means for the transmission of signals by introducing variations in its frequency in accordance with the varying characteristics of the signals to be transmitted.

frequency modulated energy and to Obtain therefrom energy having amplitude variations corresponding to impressed signals.

A further object of the invention is to provide a system capable of producing either frequency or amplitude modulated waves, or

waves having combined frequency and amplitude modulations.

Another object of this invention is to amby means of an am- A feature of the invention relates to means comprising a space path whereby the impedance of an oscillatory circuit may be varied in accordance with signals to produce corresponding frequency variations.

7 the signals to-a receiving device.

Another feature concerns an intermediate frequency amplifier havm means for compensating for the capacity etween electrodesof a three element vacuum tube to prevent sm mg. g 7

his invention may comprise transmitting and receiving systems. In the transmitting system, an oscillationgenerator, preferably of the vacuum tube type, may be coupled to an. antenna or a signaling circuit, and may have associated with its oscillation circuit tenna supplying energy to a detector that is arranged to produce oscillations difiering in frequency from those received, whereby an intermediate frequency is produced in its output circuit.

Energy of the intermediate frequency may be supplied to a vacuum tube amplifier, having a second detector coupled thereto. This detector is supplied with amplified energy from the output circuit of the am lifier and to supply energy varying in accor ance with The intermediate frequency amp preferably coupled to the output circuit of the first detector and to the input circuit of 85 the second detector by means of transformers forming portions, respectivel ,of resonant circuits of the amplifier. ese resonant circuits are tuned to the same frequency. In order to prevent singing, caused by the capacity between the grid and plate of the amplifier tube, the input or output circu1t of the amplifier is provided with means whereby the phase of the currents traversing these clrcuits may be caused to differ with respect to each other and thus prevent the establishment of parasitic oscillations.

In the figures of the drawings, transmitting and receiving systems are illustrated as ollows:

Fig. 1, a transmitting system in accordance with this invention for producing frequency modulation.

, Fig. 2, a receiving system in accordance with this invention for receiving energy modulated in accordance with frequency variations.

Fig. 3, a modification of the intermediate frequency amplifier of Fig. 2.

Like reference characters are used throughout the drawings to designate like parts.

Referring to Fig. 1, a transmitter 10, which is representative of any source of sig nal variations, is connected in a circuit including the battery 11 and the primary 12 of the transformer 13. The secondary of transformer 13 is connected in the input circuit of a vacuum tube 16, which input circuit is connected between the grid and filament of this tube. A battery 17 serves to supply glolarizing potential .to the grid of the tube.

nergy is supplied to the output circuit of tube 16, which is connected between its filament and plate, by a battery 18 connected in series with a choke coil 19. I

The oscillation generator 21 is of the type disclosed in U. S. Patent 1,356,763, October 26 1920 to Hartley. It comprises a vacuum tube 22 havin an input circuit 23, an output circuit 24, and a tuned circuit 26. The input circuit 23, connected between the grid and filament of tube 22, comprises a resistance 27 in series with a portion of the inductance 28 in the resonant circuit 26.

The filament and plate of tube 16, in series with a condenser 31, are connected to the input circuit of tube 22 in such a manner as to form a shunt path of controllable impedance between the filament and grid.

The output circuit of tube 22 comprises a second portion of theinductance 28 of resonant circuit 26 in series with a space current source consisting of a battery 32 shunted by a by-pass condenser 29. v

Resonant circuit 2-6 comprises the inductance 28 and a variable condenser33,.,-and forms a coupling between the inputand output circuits whereby oscillations are established.

An antenna 34 is coupled to the resonant circuit-26 by means of a coil35. The antenna is connected to ground through the coil 35 in series with a variable condenser 36.

. i The circuit of Fig. 1 operates as follows: Variations in the current, flowing through the primary 12 of transformer13, are produced by sound waves impressed upon the transmitter 10. vCorresponding variations are, therefore, produced in the secondary 14 of this transformer. These variations, thus introduced in the input circuit of vacuum tube 16, cause the potential of the-grid of this 16. At other values of impedance of tube 16 the frequency of oscillations remains 'substantially constant with change of this im- .pedance, but the amplitude varies rapidly. It is thus evident that the variations in the impedance of this space path may be adjusted so that variations inthe frequency or amplitude of oscillations generated by the circuit 21 may be produced as desired.

The energy of the oscillations generated in the generator 21 is supplied to the antenna 34 through the coupled inductances 28 and 35. Condenser 31 prevents the flow of direct current from battery 18 inthe-input circuit of tube 22. Condenser 29 supplies a path for the oscillatory currents about the battery 32. In Fig. 2, a receiving system is shown arranged to receive the energy transmitted from the system of Fig. 1.

An antenna 40 is connected to ground through an inductance 41 in series with a variable condenser 42.

A detector 43 has its input circuit coupledto the antenna 40 by means of an inductance 44 coupled to inductance 41 and forming a portion of a resonant circuit 46. The remaining portion of the resonant circuit 46 comprises a variable condenser 47.

I A battery 48 is connected in the input circuit of detector 49 for supplying a polarizing potential to the grid ofthis tube. The output circuit of detector 43, which comprises a connection between the filament and plate of'tube 49, includes a resonant circuit 51 consisting of a variable condenser 52 and an inductance 53. The resonant circuit 51 is in series with a feedback coil 54 and a plate battery 56.

The coil 54 is coupled to the inductances 41 and 44, whereby energy may be fed back from the output circuit to the input circuit of detector 43 for establishing heterodyne oscillations.

Resonant circuit 46 may be tuned to any desired frequency by adjusting variable condenser 471. Resonant circuit 51 may likewise be tuned by adjusting condenser 52.

An intermediate frequency amplifier 57 is arranged to amplify energy from the detector 43, The ampli er has a resonant circuit 58 connected in its input circuit across the grid and filament of the vacuum tube 59, and this resonant circuit has a coil 60 inductively coupled to the coil 53 of resonant circuit 51.. The other element of resonant circuit 58 consists of a variable condenser 61.

A grid polarizing battery 62 is in the input circuit of the tube 59 in series with resonant circuit 58. v

The output circuit of amplifier 57 includes a resonant circuit 63 and in series therewith a variable condenser 64 shunted by an impedance 65. A battery 66 is arranged to supply plate current to the tube 59. The elements of resonant circuit 63 are an inductance 67 and a variable condenser 68.

The variable condenser 64 is provided to introduce a capacity reactance in the output circuit of tube 59 in order to prevent the establishment of parasitic oscillations in the amplifier, otherwise permitted by the capacity between the grid and plate, as indicated by dotted lines. Condenser 64 has preferably a range of capacity such'that its effect upon the tuning of the amplifier is negligible,

and thus the selectivity of the circuit is unafl'ected thereby. The impedance is shunted around the condenser 64 to provide a path for direct current from battery 66. Thls 1mpedance may consist of an inductance and a resistance in series.

A second detector 69 receives energy from amplifier 57. This detector comprises a Vacuum tube 70 having an input circuit connected between its grid and filament. In this input circuit is a resonant circuit 71 coupled to the resonant circuit 63 and consisting of an inductance 72 and a variable condenser 73. The output circuit of detector 1 69 is connected between the filament and plate of tube 70 and includes a receiver 74, shunted by variable condenser 75, connected in series with a plate battery 76.

In the operation of the receiving system of Fig. 2, the antenna 40 receives energy of substantially constant amplitude having frequency modulation in accordance with signals or of substantially constant frequency but having amplitude modulations. This energy is transmitted through the coupled inductances 41 and 44 to tuned circuit 46 and is impressed upon the input electrodes of detector 43. The tuned circuit 46 is adjusted to resonance at the carrier or normal frequency of received waves.

By means of the feedback coil 54, which couples the output circuit 43 to its input circuit, oscillations are established in the detector. These oscillations may be adjusted to have any desired frequency, but are preferably made other than the frequency of received waves.

The incoming energy wilLcombine with the locally produced oscillations in the input circuit of tube 49 and produce in the output circuit of this tube currents of frequencies which comprise the sum of difference of the received frequencies and the oscillation frequency. Tuned circuit 51 is adjusted to resonance at the desired intermediate frequency represented either by the sum or difference of the carrier and locally generated oscillations.

Energy of this intermediate frequency is supplied to amplifier 57 through the inductively coupled coils 53 and 60 of resonant circuits 51 and 58. The resonant circuits 58 and 63, in the input and output circuits, respectively, of amplifier 57, are tuned to the intermediate frequency.

In order to prevent parasitic oscillations or singing in this amplifier, which may otherwise be established by virtue of the coupling between its output and input circuits supplied by the inherent capacity between the grid and plate as indicated in the dotted lines,

a condenser 64 is provided. By means of the condenser the reactance of the output circuit may be adjusted in value and, if desired, may be caused to be in the nature of a capacity reactance.

By adjusting condenser 64, the effective reactance of the output circuit may also be caused to be of sign different from the sign of the effective reactance of the input circuit, at any frequency at which oscillations tend to occur, to thereby prevent the establishment of parasitic oscillations.

The impedance 65, which is designed to obstruct the oscillatory currents, is shunted about condenser 64 to supply a path for space current from battery 66.

Amplified energy of the intermediate frequency is supplied to the second detector 69 by the coupling between coils 67 and 72 of "resonant circuits 63 and 71.

Resonant circuit 71 is tuned to the frequency represented in value approximately by the sum or difference of the intermediate frequency and the mean of the range of frequencies produced by the signal variations in the transmitter ofFig. 1.. For example, if the system of Fig. 1 produces a range of frequency variation of 4,000 cycles the mean of by the transmitter 10 at the sending station, which are applied to and actuate the receiver 7 4.

In Fig. 3 a modification of the intermediate frequency amplifier 57 is illustrated. This circuit is identical with the corresponding one shown in Fig. 2, with the exception that condenser 64 together with its shunt impedance 65 is connected in the input circuit instead of the output circuit of the amplifier. By this arrangement the phase of the current flowing in and the reactance of the input circuit are adjusted relative to that of the output circuit, for the purpose of preventing parasitic oscillationsj The impedance 65 in this instance is preferably a resistance to supply a leak path for negative charges which would otherwise accumulate upon the grid of tube 59 and block its action. No further description of this figure will be given, inasmuch as its operation is substantially identical with that of the amplifier 57 of Fig. 2.

The particular embodiment of this invention which have been illustrated and described have been chosen to show the application of the principles involved and to illustrate the features thereof and are in nowise intended to limit the scope thereof.

What is claimed is:

1. The method of modulation which comprises generating continuous single frequency oscillations of substantially constant amplitude, producing electrical waves corresponding to signals to be transmitted, and using said electrical waves to directly vary the frequency of said oscillations.

2. A modulating system which comprises a vacuum tube oscillator, a space current path forming a portion of the oscillatory circuit of said oscillator, and means for varying the impedance of said space path in accordance with signals between such limits as to produce corresponding variations in the frequency of oscillations generated, and means for maintaining the amplitude of said oscillations substantially constant.

3. The method of producing an electrical wave modulated in frequency in accordance with a signal wave by means of an oscillatory circuit and a space current path connected in shunt to at least a portion of said oscillatory circuit, which method comprises controlling, in accordance with the signal wave, the impedance of the space current path within such limits as to produce corresponding variations in the frequency of the oscillationsTgenerated in said oscillatory circuit.

4. he method of producing an electrical wave modulated in frequency in accordance with a speech wave by means of an oscillatory circuit and a space current path connected in shunt to at least a portion of said oscillatory circuit which method comprises producing an electrical wave corresponding in frequency to the speech wave, and controlling in accordance with the produced electrical wave the impedance of the space current path within such limits as to produce corresponding variations in the frequency of the oscillations generated in said oscillatory circuit.

5. The method of producing an electrical wave modulated in frequency in accordance with a lower frequency electrical wave by means of an electric discharge device having an input circuit and an output circuit coupled together through an oscillatory circuit, which method comprises controlling the effective coupling between said oscillatory circuit and said input circuit in accordance with the wave of lower frequency so as to vary the instantaneous frequency of the oscillations in the output circuit.

6. A modulating system comprising a vacuum tube oscillator including an oscillatory circuit, an electric discharge device having a space current path associated with said oscillatory circuit, and means for varying the impedance of said space current path in accordance with signals between such limits as to produce corresponding frequency variations of the oscillations generated.

In witness whereof, I hereunto subscribe my name this 27th day of November A. D.,

LEON J. SIVIAN. 

